The present invention relates to: a chromium-free liquid metal surface treatment composition that forms, by spontaneous chemical reaction with a metal surface, a treatment coating with superior corrosion resistance, alkali resistance and fingerprint resistance; a metal surface treatment process that uses the treatment composition according to the invention; and articles of manufacture comprising metal surfaces treated by a process according to the invention. Suitable substrates for the invention include, but are not limited to, molded metal articles, cast metal articles, and metal sheet, coils, and the like that are used for automobile bodies, construction materials, household electrical appliances, and the like. Preferred metallic surfaces for treatment according to the invention are zinc- and zinc alloy-coated steel, uncoated (non-stainless) steel, and aluminum.
Metal surfaces such as these readily become corroded as a result of being oxidized by oxygen in the atmosphere, moisture, ions contained in moisture, etc. Conventional methods used to prevent such corrosion have included depositing a chromate coating film on the metal material by causing the surface of the metal material to contact a treatment solution containing chromium in the form of chromic acid, at least one chromate, etc. Such an inorganic chromate coating film alone exhibits short-term anti-corrosion properties in relatively mild environments but has insufficient long-term corrosion resistance and/or corrosion resistance in harsher environments. Furthermore, when sheets or coils treated with chromate alone are cut and/or molded, the molded coating film is usually hard and brittle and lacks facile slipping properties. As a result, not only can the coating film fall off so that the external appearance suffers, but sufficient working often can not be performed without generating cracks in the material. In addition, fingerprints of workers handling the metal adhere to its surface during working, and traces of these fingerprints remain even after degreasing and cleaning, so that there is a further adverse effect on the external appearance. Accordingly, in order to satisfy all performance requirements in terms of high corrosion resistance, fingerprint resistance, scratch resistance, slip properties, and paint adhesion, etc., a two-layer treatment is generally performed in which a chromate coating film is formed on the surface of the metal material, and a resin coating film is formed over the surface of this chromate coating film. Furthermore, in addition to being inadequate in terms of performance, a chromate coating film involves trouble and expense in terms of waste water disposal, since the treatment solution contains polluting hexavalent chromium. Moreover, since the formed coating film also contains hexavalent chromium, such chromate coating films tend to be avoided from the standpoints of safety and environmental considerations.
Resin chromates in which a chromate and a resin coating film are formed at one time have been investigated in an attempt to satisfy all performance requirements using a single-layer treatment. A treatment method in which the surfaces of aluminum-galvanized steel plates are coated with a resin composition containing a specified water-dispersible or water-soluble resin and a specified amount of hexavalent chromium is disclosed in Japanese Patent Application Kokoku No. 4-2672, and a metal surface treatment composition which contains hexavalent chromium ions or hexavalent chromium ions and trivalent chromium ions of an inorganic compound and an acrylic emulsion polymerized under specified emulsion polymerization conditions is disclosed in Japanese Patent Application Kokoku No. 7-6070. However, although the amounts of hexavalent chromium contained in these coating films is small, this hexavalent chromium is gradually eluted from the coating films, so that there are problems in terms of environmental and safety considerations as described above.
In regard to methods which use a treatment solution that contains no chromium: A polymer composition used for the surface treatment of metal materials which contains a phenol resin type polymer with a specified structure and an acidic compound, and a surface treatment method using this composition, are disclosed in Japanese Patent Application Kokai No. 7-278410; a metal surface treatment agent which contains two or more types of silane coupling agents that have reactive functional groups with specified structure capable of reacting with each other and with other types of groups, and which is superior in terms of fingerprint resistance, etc., and a treatment method using this metal surface treatment agent, are disclosed in Japanese Patent Application Kokai No. 8-73775; a metal surface treatment agent which contains a silane coupling agent that has a specified structure and a phenol resin type polymer that has a specified structure, and a treatment method using this metal surface treatment agent, are disclosed in Japanese Patent Application Kokai No. 9-241576; a metal surface treatment agent which contains a specified polyvalent anion and an organic polymer such as an epoxy resin, acrylic resin or urethane resin, etc., that has at least one nitrogen atom per molecule, a treatment method using this metal surface treatment agent and a treated metal material are disclosed in Japanese Patent Application Kokai No. 10-1789; and (i) an anti-rust agent which contains a bisphenol A epoxy type resin with a specified structure, and (ii) an anti-rust agent which contains a phenol type resin and another specified resin such as a polyester, etc., at a specified ratio, as well as a treatment method using (i) and (ii), and a treated metal material, are disclosed in Japanese Patent Application Kokai No. 10-60233.
However, although metal surface treatments that do not use chromium are advantageous in that the treatment solution contains no hexavalent chromium, the corrosion resistance produced by such treatments is often insufficient, and in particular, the corrosion resistance obtained in scratched parts and worked parts is conspicuously inferior to that afforded by chromate coating films. Moreover, the fingerprint resistance, scratching resistance and slip properties usually are also insufficient.
At the present time, therefore, no non-chromate type metal surface treatment agent capable of forming a coating film that simultaneously endows the surfaces of metal materials with superior corrosion resistance, alkali resistance and fingerprint resistance has yet been obtained, insofar as the applicants are aware.
The major object of this invention is to provide a metal surface treatment composition that does not contain chromium and endows metal materials with at least one of corrosion resistance, alkali resistance, and fingerprint resistance that are superior to those obtained by prior art chromate-free compositions, along with a process for using this metal surface treatment composition and with articles of manufacture resulting therefrom.
It has been found that a coating film which has superior corrosion resistance, alkali resistance and fingerprint resistance can be obtained by treating the surface of a metal material with a metal surface treatment composition that contains a resin with a specified structure, a vanadium compound, and a specified metal compound as essential components.